Effects of inulin on growth performance and intestinal health of broilers by modulating intestinal microbiota and metabolome

Inulin, a natural dietary fiber, confers multiple physiological benefits. However, the effects of inulin on the liver and intestinal health of broilers remain unclear. The study investigated the effects and mechanisms of inulin supplementation on hepatic and intestinal health of broilers. A total of 192 male broilers (821.15 ± 14.99 g) at 21 d of age were randomly allocated to four treatment groups, comprising eight replicates per group with six broilers each. The dietary treatments included: a control group (CON) receiving a basal diet and three treatment groups fed the basal diet supplemented with 0.5, 1.0, or 2.0 g/kg inulin (designated as INU-0.5, INU-1.0, and INU-2.0, respectively). Results indicated that dietary inulin supplementation elicited a quadratic response in final body weight (FBW, <i>P</i> = 0.032). Inulin supplementation produced linear improvements in average daily gain (ADG, <i>P</i> = 0.044) alongside quadratic reductions in both average daily feed intake (ADFI) and feed-to-gain ratio (F/G ratio) (<i>P</i> < 0.001). Notably, inulin supplementation linearly decreased malondialdehyde (MDA) levels (<i>P</i> < 0.001) while significantly enhancing superoxide dismutase (SOD) activity (<i>P</i> < 0.001). Furthermore, inulin supplementation demonstrated dose-dependent effects on lipid metabolism, including a linear reduction in abdominal fat deposition (<i>P</i> < 0.001), decreased hepatic and serum concentrations of total cholesterol (TCHO, both <i>P</i> < 0.001) and triglycerides (TG, <i>P</i> < 0.001 and <i>P</i> = 0.001, respectively), and reduced serum levels of both high-density lipoprotein (HDL, <i>P</i> = 0.010) and low-density lipoprotein (LDL, <i>P</i> < 0.001) (<i>P</i> < 0.01). Parallel improvements in intestinal barrier function were observed, with linear increases in jejunal expression of tight junction proteins (claudin-5, occludin, and zonula occludens-1 [ZO-1]), mucin 2 (MUC2), and diamine oxidase (DAO) (<i>P</i> < 0.001). Additionally, inulin supplementation selectively increased the abundances of key microbes, including <i>Bacteroides</i>, <i>Lactobacillus</i>, and <i>Akkermansia</i>, while decreased the abundances of <i>Alistipes</i>, <i>Odoribacte</i>, <i>Parabacteroides</i>, <i>Rikenella</i>, and <i>Erysipelatoclostridium</i> (<i>P</i> < 0.001). These microbial shifts were associated with modulation of key metabolic pathways, including taurine and hypotaurine metabolism, purine metabolism, arginine and proline, and phenylalanine metabolism. Collectively, these findings demonstrate that inulin supplementation enhances broiler productivity while improving both intestinal and hepatic health (<i>P</i> < 0.05) through microbiota-mediated metabolic regulation. Therefore, dietary inulin supplementation would be a recommendable nutritional strategy to optimize production efficiency in commercial broiler industry.